The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Combustion phasing, or the time in an engine cycle when combustion in a cylinder occurs, affects the time when the cylinder produces its peak torque. Combustion phasing of a cylinder may be characterized by a crank angle at which the cylinder burns 50 percent of the fuel in the cylinder, which may be referred to as crank angle 50 (CA50). Engine controls systems control the CA50 of each cylinder of an engine in order to control the time when each cylinder produces its peak torque, and thereby balance the engine.
Engine control systems control the CA50 of a cylinder by adjusting the spark timing of the cylinder to minimize a difference between a desired CA50 and an estimated CA50. Engine control systems estimate the CA50 of a cylinder by measuring the pressure in the cylinder during an engine cycle and determining the total amount of heat released due to combustion in the cylinder during the engine cycle based on the measured cylinder pressure. The CA50 of a cylinder may be approximately equal to a crank angle at which 50 percent of the total amount of heat is released. Thus, engine control systems determine the crank angle at which 50 percent of the total amount of heat is released based on the total amount of heat released and a rate of heat release, and set the CA50 equal to the crank angle determined.
Estimating the CA50 of each cylinder of an engine in the manner described above requires a pressure sensor in each cylinder and involves a large computation burden, which can lead to a poor response time when controlling the CA50 of each cylinder. This poor response time decreases the effectiveness of the CA50 control, which can lead to cylinder imbalance and thereby decrease fuel efficiencies and degrade vehicle durability and drivability. In addition, the need for a pressure sensor in each cylinder increases manufacturing costs and may cause reliability issues.